The present invention relates to methods and compositions for inhibiting corrosion, and more particularly relates, in one embodiment, to methods and compositions for inhibiting corrosion employing mercaptoalcohols.
It is well known that steel tubulars and equipment used in the production of oil and gas are exposed to corrosive environments. Such environments generally contain acid gases (CO2 and H2S) and brines of various salinities. Under such conditions the steel will corrode, possibly leading to equipment failures, injuries, environmental damage and economic loss. Further in some cases, drilling fluids have acid intentionally added thereto in order to acidize the formations to enhance hydrocarbon recovering. This added acid also causes corrosion problems.
While the rate at which corrosion will occur depends on a number of factors such as metallurgy, chemical nature of the corrosive agent, salinity, pH, temperature, flow rate, etc., some sort of corrosion almost inevitably occurs. One way to mitigate this problem consists of using corrosion inhibitors in the hydrocarbon production system.
It is known in the art that the corrosion of iron and iron-based alloys such as steel alloys in contact with oil-in-brine emulsions can be inhibited by treating the emulsions with oil soluble, water soluble or water-dispersible nitrogen-containing, phosphorus-containing and/or sulfur-containing corrosion inhibitors. Not all corrosion inhibitors perform acceptably in all applications, e.g. severe applications such as high shear and high flow rate environments. Current technology for high shear/high flow applications also includes mercaptocarboxylic acid (e.g. mercaptoacetic acid) used with other conventional corrosion inhibitors (e.g. imidazolines).
Broad statements like those in U.S. Pat. No. 3,462,496 that mercaptoalcohols are known to be useful as corrosion inhibitors are not helpful in directing one having ordinary skill in the art to choosing which compositions would be effective as corrosion inhibitors in particular applications. For instance, one of ordinary skill in the art would not know which compounds would be useful in protecting copper or steel or other iron alloys in contact with aqueous or hydrocarbon environments over particular temperature or pressure ranges, and the like, based only upon such very sparse teachings. The minimal instruction of U.S. Pat. No. 3,462,496 also does not teach the importance that the mercaptoalcohols should be water soluble in certain environments.
It would be advantageous if a new corrosion inhibitor were discovered that would be an improvement over the presently known systems.
Accordingly, it is an object of the present invention to provide a corrosion inhibitor composition that is effective in inhibiting the corrosion of steel surfaces in oil field tubing and equipment, particularly both general and localized corrosion.
It is another object of the present invention to provide a water-soluble corrosion inhibitor that has relatively poor chelation of and lower solubility of iron complexes, as well as increased film persistence.
In carrying out these and other objects of the invention, there is provided, in one form, a corrosion inhibitor composition having at least one mercaptoalcohol.
FIG. 1a is a graph of corrosion inhibition (%) measured by linear polarization resistance (LPR) for seven different sulfur-containing corrosion inhibitor candidates and an imidazoline reference material as a function of concentration;
FIG. 1b is a graph of corrosion inhibition (%) measured by weight loss for the seven different sulfur-containing corrosion inhibitor candidates and the imidazoline reference material of FIG. 1a as a function of concentration;
FIG. 1c is a graph of corrosion inhibition (%) measured by iron count for the seven different sulfur-containing corrosion inhibitor candidates and the imidazoline reference material of FIG. 1a as a function of concentration;
FIG. 2 is a graph of corrosion inhibition (%) measured by LPR, weight loss, and iron count from FIGS. 1a-1c for the seven best-performing sulfur-containing corrosion inhibitor candidates at a concentration of 1.0 ppm;
FIG. 3 is a graph of corrosion inhibition (%) measured by LPR, weight loss, and iron count for 2ME, DTDPA, and TGA in brine at a concentration of 1.0 ppm; and
FIG. 4 is a graph of corrosion inhibition (%) measured for 2ME and 1-mercapto-2-propanol under identical conditions.